Thanks, that helps a lot. I will talk to them in due time about everything and see where it goes.
We're a very tight nit group and we're all very open with our sexuality. I would probably be okay with it if my best friend was okay with it. They are rather annoyed/bored with each others sexual/emotional needs which is why they're trying poly.
Knowing him, I think he'd rather it be someone he knows then somebody random.